Hybrid super-capacitor / rechargeable battery system

ABSTRACT

A hybrid system modifies a control algorithm such that the super-capacitor can not only supply pulsed power, but it now can also absorb pulsed power from the load while keeping the battery current constant such that the incoming pulsed power does not stress the battery. The absorbed energy is accumulated in the capacitor and then the control algorithm operates the DC/DC converter to recharge the battery with the energy from the capacitor at a rate that optimized battery performance. If the load supplies energy to the hybrid system such that the current into the battery is within its optimal operating range, then the load is permitted to directly charge the battery. This hybrid system keeps the battery current operating in its most efficient range during both discharging and charging (the discharging and charging currents may be different values) by using the super-capacitor to supply or absorb pulsed in energy that would otherwise stress the rechargeable battery and result in reduced battery cycle life and/or reduced effective capacity over time.

RELATED APPLICATIONS

This application is a Continuation-in-part of U.S. application Ser. No.14/279,687 filed May 16, 2014, pending, which claims the benefit of U.S.Provisional Application 61/824,988 filed May 17, 2013

BACKGROUND OF THE INVENTION Field of Invention

The present invention relates generally to the field of battery systems.More specifically, the present invention is related to a novel designfor hybrid super-capacitor/battery systems in pulsed power applications.

Discussion of Related Art

Super-capacitors are specialized low voltage capacitors with very highcapacitance in a relatively small size. These devices provide superiorenergy, power density and capability compared to standardly availablecapacitors based on older technologies. Several types ofsuper-capacitors are commercially available including Electric DoubleLayer Capacitors (EDLCs) and Lithium Ion Capacitors (LiCs). Such devicesare finding uses in automotive, power backup and consumer electronicsapplications, and are viable replacements for flywheels inenergy-storage and bridge-power systems.

The key advantages of the super-capacitor technology over batterytechnology are the long lifetime, low leakage and high cycle life, alongwith much greater pulsed power capability for both charging anddischarging. Battery technology still offers better energy storagedensity than super-capacitors but batteries can't compete with the powerdensity, and lifetime advantages they provide.

Given the complementary capabilities of batteries and super-capacitors,there is a need in pulsed power applications for the incorporation of ahybrid approach using a combination of super-capacitors and batteries tooffer the best performance while considering system cost and performanceat the same time.

Embodiments of the present invention are an improvement over prior artsystems and methods.

SUMMARY OF THE INVENTION

In one embodiment, the present invention provides a system comprising: ahybrid super-capacitor/battery system comprising a super-capacitor unitcomprising one or more super-capacitors and a battery unit connected toa load, the battery unit comprising one or more battery cells rated at abattery output voltage; a DC/DC converter connected to saidsuper-capacitor unit and said battery unit, the DC/DC converter allowingcharging and discharging of said super-capacitors; and a hybridalgorithm comprising: a battery management system, a super-capacitormanagement system, a load management system, and a hybrid controller,the battery management system collecting a first set of data comprisingvoltage, current, and temperature measurements associated with thebattery unit, and identifying a state and health of the battery unitbased on the first set of data, the super-capacitor management systemcollecting a second set of data comprising voltage and temperaturemeasurements associated with the super-capacitor, and determining asuper-capacitor state and health based on the second set of data, theload management system collecting a third set of data comprising voltageand current data associated with the load, and determining a state ofthe load based on the third set of data, the hybrid controller samplingsystem measurements available through the battery management system, thesuper-capacitor management system, and the load management system, andmanipulating the DC/DC converter to control power flow, whereinintegration of the battery management system, the super-capacitormanagement, and the load management system with the hybrid controllerroutes bidirectional power and energy such that battery stress isreduced (the battery stress is reduced by keeping the charging and thedischarging current within optimal range of the battery; the currentlevels are not necessarily the same for charging and discharging), andsystem performance is optimized, and wherein the system is effectivewhether it is supplying or absorbing energy.

In another embodiment, the present invention provides a systemcomprising: a hybrid super-capacitor/battery system comprising asuper-capacitor unit comprising one or more super-capacitors and abattery unit connected to a load, the battery unit comprising one ormore battery cells rated at a battery output voltage; a DC/DC converterconnected to said super-capacitor unit and said battery unit, the DC/DCconverter allowing charging and discharging of said super-capacitors;and a hybrid algorithm comprising: a battery management system, asuper-capacitor management system, a load management system, and ahybrid controller, the battery management system collecting a first setof data comprising voltage, current, and temperature measurementsassociated with the battery unit, and identifying a state and health ofthe battery unit based on the first set of data, the super-capacitormanagement system collecting a second set of data comprising voltage andtemperature measurements associated with the super-capacitor,determining a super-capacitor state and health based on the second setof data, and, based on collected second set of data, determining whenenergy should be sourced or sinked, the load management systemcollecting a third set of data comprising voltage and current dataassociated with to the load, and determining a state of the load basedon the third set of data, the hybrid controller sampling systemmeasurements available through the battery management system, thesuper-capacitor management system, and the load management system, andmanipulating the DC/DC converter to control power flow, whereinintegration of the battery management system, the super-capacitormanagement, and the load management system with the hybrid controllerroutes bidirectional power and energy such that battery stress isreduced (the battery stress is reduced by keeping the charging and thedischarging current within optimal range of the battery; the currentlevels are not necessarily the same for charging and discharging), andsystem performance is optimized with regards to any of, or a combinationof, the following parameters: cycle life, effective capacity, andreduced operating temperature, and wherein the system is effectivewhether it is supplying or absorbing energy.

In yet another embodiment, the present invention provides a systemcomprising: a hybrid super-capacitor/battery system comprising asuper-capacitor unit comprising one or more super-capacitors and abattery unit connected to a load, the battery unit comprising one ormore battery cells rated at a battery output voltage; a DC/DC converterconnected to said super-capacitor unit and said battery unit, the DC/DCconverter allowing charging and discharging of said super-capacitors;and a storage medium comprising computer readable program code whichwhen executed by a processor implements a hybrid algorithm comprising: abattery management system, a super-capacitor management system, a loadmanagement system, and a hybrid controller, the storage mediumcomprising: computer readable program code which when executed by theprocessor implements the battery management system collecting a firstset of data comprising voltage, current, and temperature measurementsassociated with the battery unit, and identifying a state and health ofthe battery unit based on the first set of data, computer readableprogram code which when executed by the processor implements thesuper-capacitor management system collecting a second set of datacomprising voltage and temperature measurements associated with thesuper-capacitor, determining a super-capacitor state and health based onthe second set of data, and, based on collected second set of data,determining when energy should be sourced or sinked, computer readableprogram code which when executed by the processor implements the loadmanagement system collecting a third set of data comprising voltage andcurrent data associated with the load, and determining a state of theload based on the third set of data, computer readable program codewhich when executed by the processor implements the hybrid controllersampling system measurements available through the battery managementsystem, the super-capacitor management system, and the load managementsystem, and manipulating the DC/DC converter to control power flow,wherein integration of the battery management system, thesuper-capacitor management, and the load management system with thehybrid controller routes bidirectional power and energy such thatbattery stress is reduced (the battery stress is reduced by keeping thecharging and the discharging current within optimal range of thebattery; the current levels are not necessarily the same for chargingand discharging), and system performance is optimized with regards toany of, or a combination of, the following parameters: cycle life,effective capacity, and reduced operating temperature, and wherein thesystem is effective whether it is supplying or absorbing energy.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure, in accordance with one or more various examples,is described in detail with reference to the following figures. Thedrawings are provided for purposes of illustration only and merelydepict examples of the disclosure. These drawings are provided tofacilitate the reader's understanding of the disclosure and should notbe considered limiting of the breadth, scope, or applicability of thedisclosure. It should be noted that for clarity and ease of illustrationthese drawings are not necessarily made to scale.

FIG. 1 illustrates a non-limiting example of a hybrid system accordingto the teachings of the present invention.

FIG. 2 depicts an overview of the system feedback control model forforward boost, reverse buck converter.

FIG. 3 illustrates the bidirectional power converter circuitry accordingto one embodiment of the present invention.

FIG. 4 illustrates the three-phase converter topology according to oneembodiment of the present invention.

FIG. 5 illustrates the three-phase converter current waveform withinterleaved operation according to one embodiment of the presentinvention.

FIG. 6 illustrates the switch controller with interleaved closed loopcurrent controllers and PWM according to one embodiment of the presentinvention.

FIG. 7 illustrates a second embodiment of a non-limiting example of ahybrid system according to the teachings of the present invention withoutput dc/dc converter that allows a range of output load voltages.

FIG. 8 depicts an overview of the system feedback control model forforward boost, reverse buck operation with outer current controller andwithout inner loop voltage controller.

FIGS. 9A-D illustrate preferred embodiments of the hybridsuper-capacitor/battery system for portable power application. TheBA-5590 is battery-only standard portable power unit. Other power unitscan be applied in a similar way. FIG. 9A shows the standard BA-5590connected to a load device. FIG. 9B illustrates a non-limiting exampleof the hybrid system taught here replacing the standard BA-5590 batterysystem. The super-capacitor/batteries are integrated into a portablepower hybrid system. FIG. 9C illustrates the hybrid power system taughthere but with the hybridization achieved with a standard BA-5590connected to an external Hybrid Module, which in turn is connected tothe load device. FIG. 9D illustrates the hybrid power system taught herebut with the hybridization achieved with the standard BA-5590 connectedto a load device, with such load device incorporating the hybridizationmodule.

FIG. 10 illustrates the success of the hybrid super-capacitor/batteriessystem in extending the discharge lifetime of batteries during a pulsedpower load.

FIG. 11 shows a preferred embodiment of the hybridsuper-capacitor/batteries system that is the same form and fitreplacement for a standard BA-5590 battery pack.

FIG. 12 depicts the basic elements of a hybrid system.

FIG. 13 shows the hybrid algorithm structure and interconnection withinthe hybrid system.

FIG. 14A-M illustrate valid hybrid system energy flow states.

FIG. 15 shows the energy density distribution for the alkaline chemistrydistribution as a function of discharge rate and ambient temperature.

FIG. 16 shows improved discharge capacity using they hybrid approachcompared to the battery-only approach.

FIG. 17 depicts improvement of charge capacity using the hybrid approachcompared to the battery-only approach.

FIG. 18 depicts improvement in temperature (battery cooler) using thehybrid approach compared to the battery-only approach.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

While this invention is illustrated and described in a preferredembodiment, the invention may be produced in many differentconfigurations. There is depicted in the drawings, and will herein bedescribed in detail, a preferred embodiment of the invention, with theunderstanding that the present disclosure is to be considered as anexemplification of the principles of the invention and the associatedfunctional specifications for its construction and is not intended tolimit the invention to the embodiment illustrated. Those skilled in theart will envision many other possible variations within the scope of thepresent invention.

Note that in this description, references to “one embodiment” or “anembodiment” mean that the feature being referred to is included in atleast one embodiment of the invention. Further, separate references to“one embodiment” in this description do not necessarily refer to thesame embodiment; however, neither are such embodiments mutuallyexclusive, unless so stated and except as will be readily apparent tothose of ordinary skill in the art. Thus, the present invention caninclude any variety of combinations and/or integrations of theembodiments described herein.

The Hybrid Super-Capacitor/Battery System Concept

The basic idea of the hybrid super-capacitor/battery (HSCB) concept isto use the power (and other) capabilities of the super-capacitors toaugment the good energy capability of batteries, and provide systemperformance with the best of both devices. Essentially, high-powershort-duration pulses would be supplied by capacitors, while batterieswould supply the overall average power and energy demands of the load.In this way, thermal stresses and energy loss are minimized in thebattery. This approach will always result in greater battery capacity,lifetime and number of charge/discharge cycles. This benefit comes withthe addition of super-capacitors and support circuitry, which adds costand complexity to the system. However, depending on the application,these factors can be offset by cost, weight and space savings when thenumber of battery cells can be substantially reduced, as well as thefuture cost savings due to longer battery life. In applications wherecost and space/weight are not primary concerns, the hybrid approachprovides a way to keep the same number of battery cells, which allowsthe batteries to provide even longer runtime (i.e. greater energycapacity), while providing overall better system specifications byenhancing the pulsed power capability.

The use of both super-capacitors and battery cells, with their verydifferent voltage levels and discharge profiles, requires a DC/DCconverter system capable of bidirectional energy flow to allow bothcharging and discharging of the super-capacitors. This allows efficientenergy transfer between the super-capacitors and battery cells, in asuitably configured system. In pulsed power applications, the use of ahybrid approach (particularly under high pulsed power and lowtemperature conditions) allows the existing battery system to ridethrough transient loading and provide excellent energy density and powerdensity under practical loading conditions.

FIG. 1 illustrates a block diagram of one design topology for the hybridbattery system. It should be noted that other design topologies are alsopossible, and that the setup depicted in FIG. 1 is provided as anon-limiting example for discussion purposes. A feature of this topologyis that the battery connection is directly available to the load. Inthis example, the system is controlled by a microprocessor or microcontroller 108, preferably an ultra-low power microprocessor or microcontroller 108, which allows low power monitoring modes withoutsignificantly draining the battery energy. Once a power load is appliedto the battery 102, the microprocessor or micro controller 108 quicklyactivates and enables an advance control mode. With monitoring of theenergy states of the super-capacitor block 104 (which, in a non-limitingexample, could be a Lithium Ion Capacitor (LIC) cell bank in seriesand/or parallel combination) and battery banks 102, as well as thetemperatures, load voltages and currents, the DC/DC converter 106 isable to provide the optimum power delivery from the battery 102 and thesuper-capacitor block 104. When the power load-conditions are lightenough, the capacitors in the super-capacitor block 104 automaticallyrecharge, via the DC/DC converter 106 in a reverse energy flow mode. Inthis setup, the super-capacitor block 104 discharges in a forward energyflow mode. The microprocessor or micro controller 108 allows theincorporation of advanced decision making based on existingenvironmental and load conditions. FIG. 7 illustrates a block diagram ofanother design topology for the hybrid battery system that adds anoutput dc/dc converter to the topology of FIG. 1. A feature of thistopology is that the output voltage of the system is not constrained bythe output voltage of the Battery Cell bank and can be set by the dc/dcconverter as appropriate for varied load requirements.

Importance of Advanced Control Algorithms in HSCB Systems

Hybrid use of super-capacitors with batteries, along with proper systemcontrol, will provide much improved overall power performance in pulsedpower applications. From a performance point of view, there are no realdisadvantages to the hybrid approach since a properly configured andcontrolled system will disable the super-capacitor support incircumstances when it does not provide advantages. However, this leadsto a key point that proper control requires its own innovations, anduseful approaches are not obvious.

To highlight this point, consider a simple control scheme in which thebattery current (or alternatively a power set-point could be used) isheld to a constant value by the control system. The current-set-point(or power-set-point) would be tuned to a value optimized for a givenpower load profile for the particular load on the particular system.This is important to make sure that the average power or total energyfrom the batteries is sufficient to power the load over a long period.The reason this is important is that the batteries are the energy sourceand the super-capacitors are used to provide the power during the highpower pulse periods. Thus, the battery output current (and power) iseither used to drive the load, or to recharge the super-capacitors. Ifthe load power is low and the super-capacitors are already fullycharged, then that would be the only condition where the battery is notsupplying the full current (or power) output specified by the controlset-point. This approach will surely provide load leveling for thebattery and give many benefits for lifetime and reliability of thesystem. However, if the power pulses are not large enough, then thehybrid system may waste energy (as heat in the DC/DC converter). Thisloss of capacity may not always be desirable, despite the othersignificant benefits offered.

The above effect can be explained in a simple way. Basically, the hybridapproach is able to relieve a significant amount of the heat loss in abattery (dissipated by the internal battery resistance). However, theDC/DC converter itself has its own heat loss (due to efficiency limits).In addition, the value of the peak power pulses is what determineswhether the loss in the converter is less than the loss in the battery.Above a certain power pulse threshold, the hybrid approach gives morecharge and energy capacity than the battery would provide on its own.However, below this threshold, the battery alone would have more chargeand energy capacity.

This highlights why a more advanced control scheme can provide betteroverall performance when compared to a simple set-point based controlscheme. The simple scheme will blindly charge and discharge thesuper-capacitors without regard to whether the power load profile issuitable to allow the hybrid approach to give all of the benefits,including increased charge capacity and energy capacity for the system.A more advanced control scheme would have the ability to disable thehybrid control function and allow the battery to run alone duringperiods where there are no power pulses or during periods where thereare only low-power pulses that are not large enough to allow the hybridapproach to give the best system capacity.

Improved Control Algorithm for HSCB Systems

The hybrid battery system has two key requirements to be addressed bythe system controller. First, there is a voltage specification that theoutput must maintain to be usable in the application. Second, there isthe requirement to control and balance the battery current, whilesimultaneously providing the needed load current (and voltage). Due tothese two requirements, the proposed control scheme is to use twofeedback loops. An inner voltage control loop, operating at fasterspeed, provides control of the load voltage to maintain a commandedvalue in the required range, and (provided the limits are not violated)to further regulate the voltage near the battery output voltage, whichvaries in time as the battery drains. An outer current control loop,operating at slower speed provides the voltage command, when the limitsare not violated, while controlling the battery current to apredetermined set-point based on the required operating conditions. Itcan be noted the two required functions of voltage regulation andcurrent load leveling are both achieved with fast transient response.The current set-point is as described above, and allows the batteryoutput to be load-leveled and allows the super-capacitors to provide thepulsed power needed by the load. If a simple constant value is used,then the system functions as described, although there is a possibilityfor small power pulses to cause the hybrid system to have lower charge-and energy-capacity than the battery operating alone. However, an toimprovement to the control system can be made by having hysteresis inthe current set-point. This means that two values are specified and thecontroller does not allow the super-capacitors to power the load unlessthe load current is above the higher set-point value. Then, thecontroller does not allow the super-capacitors to be recharged until theload power is below the lower set-point value. In this way, the hybridsystem can only operate when it will provide improved charge-capacityand improved energy capacity in comparison to the battery operatingalone.

Note that the system could be operated with a single control loopregulating the battery current only. This works and will (in principle)maintain both current and voltage to the proper levels. However, due tocontroller bandwidth limits and the greater difficulty in controllingcurrent at high speed, there is significant risk of the singlecontroller transient response allowing the voltage to violate thespecified voltage limits, since this method provides no ability tomonitor and control the voltage directly. Basically, a dual feedbackloop offers advantages over a direct control of current with onefeedback loop. The voltage control loop is easier to operate at fasterspeed, and there is a need to meet voltage specifications duringtransients, and this requirement overrides any longer term requirementto balance current loading. The super-capacitor energy is more thansufficient to handle short-term current surges to help keep voltageunder control, and any voltage dip limit at the load defines animmediate failure of the system. If direct current control is used,there is no guarantee that transients won't allow the output voltage togo outside the allowed specifications The typical transient responsetime of the voltage control loop should be adequate to maintain the loadvoltage range.

FIG. 2 depicts a block diagram of the proposed dual voltage/currentfeedback loop. The diagram indicates that the controller is a digitaldiscrete time system with discrete time indicated by n. A moderatelyhigh-speed PWM frequency is used to provide a good compromise betweenthe size of magnetic components and conversion efficiency. The PWMgenerator allows a discrete number of steps (i.e. the quantizer) anddrives MOSFET switches to control the system duty cycle. The diagramshows the separate control sections for voltage and current, and bothfeedback loops use PI controllers, although other types of controllerscan also be applied. Referencing the PI Voltage Controller subsystem,the blocks labeled G_(PV), Integrator, and G_(IV) form the PI controllerfor the voltage control loop, with G_(PV) being the proportional gainand G_(IV) being the integral gain. Referencing the PI CurrentController subsystem, the blocks labeled G_(PC), Integrator, and G_(IC)form the PI controller for the current control loop, with G_(PC) beingthe proportional gain and G_(IC) being the integral gain. The blockslabeled LPF are low pass filters used prior to sampling the inputsignals. The ZOH blocks are zero order holds and are typical sample andhold operation of a digital controller. The Saturation with enableblocks are signal limiters that only allow the input signal to passthrough the block if it is within the prescribed maximum and minimumvalues. Otherwise, the output of that block is limited to the maximum orminimum value allowed. The Switch Controller subsystem features a PWMgenerator which generates varying duty cycle switching commands based onthe input signal D[n]. The switching commands operate the Switches inthe Bi-directional Switching Converter subsystem. The switches controlthe flow of current between the battery, super-capacitors, and load. Thesystem monitors the capacitor bank voltage and uses it to provide a feedforward signal into the voltage controller. The battery current ismonitored and used as the input measurement for the current controller,while the load voltage is monitored and used as the input measurementfor the voltage controller. Relevant filtering and sampling are asshown.

Typically, the controller sample frequency F_(control) would be at amultiple sub-division of the PWM frequency F_(switch). It can be seenthat the controller must generate the PWM signal s(t) in order to drivethe switches. However, the controller itself needs to only generate theduty cycle D[n], and a PWM generator can generate the actual analogsignal. The duty cycle D[n] and switch control signal s(t) are relatedto each other by the following mathematical formulas, noting thatn=└t·F_(control)┘, where the half bracket/bar notation means the floorfunction, or rounding down to the lower integer value.

${D\lbrack n\rbrack} = {\left. {F_{conrol} \cdot {\int_{\frac{n}{F_{control}}}^{\frac{n + 1}{F_{control}}}{{s(t)} \cdot {dt}}}}\Leftrightarrow{s(t)} \right. = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu} \left( {{t \cdot F_{switch}} - \left\lfloor {t \cdot F_{switch}} \right\rfloor} \right)} \geq {D\lbrack n\rbrack}} \\1 & {otherwise}\end{matrix} \right.}$

This system has a PWM generator that is capable of generating aparticular quantization of discrete duty cycles in the range of 0 to 1.This resolution limit can introduce noticeable variation of the outputcontrol if the resolution in the quantizer is too low, hence some effortcould be made to ensure adequate resolution, or allow the PWM generatorto alter the duty cycle during the discrete time interval n, so that theaverage duty cycle takes on fraction values between the allowedresolution steps.

The command for the PWM generator is limited by a saturation-block. Thelimits are set at 0.05 and 0.95, but these limits are broader thanneeded and should actually be tuned as appropriate for the particularapplication. For example, a tolerance band around the feed forward valuecan be used. The saturation block generates an enable signal for theintegrator, which halts integration if a limit is hit. The controllermust also monitor several circuit variables by sampling with A/Dconverters at the controller rate, and each of the two controllers isdigitally implemented as PI controllers, as shown. The inner voltagecontrol loop monitors the load voltage to maintain the voltage at thevalue commanded by the outer current control loop. If the currentcontrol loop tries to command values outside the allowed voltage range,the saturation block limits the command (range is V_(low) to V_(high))and disables the integrator. The outer current control loop monitors thebattery current to maintain a level current draw from the battery.

Both PI controllers also utilize a feed forward signal to improve systemresponse but the feed forward may be omitted in less demanding controlapplications. The inner voltage loop uses the commanded output voltageand the value of the input capacitor voltage to estimate the typicalduty cycle that would be needed to generate that output voltage underthose conditions. It can be seen that the calculation of estimated dutycycle is simply the ratio of output voltage to input voltage, as istypically expected in a boost converter. The outer current control loopuses an estimated value or typical value for the commanded voltage. Inthis implementation, the feed forward value is just a pre-storedconstant V_(ff); however, a real system could keep a record of theestimated remaining battery capacity (by monitoring and integratingbattery current, with considerations for temperature etc.) and usemeasured battery temperature, along with a formula or look-up table toestimate the expected output voltage. The outer current loop also uses acommanded current value, which can be a pre-stored value based on theexpected load profile, or could be an adjustable value by the user.Essentially, a real implementation can use the microcontroller toprovide additional intelligence to aid the feedback loops in performingtheir functions.

It should be noted that the controller in FIG. 2 has an input commandvalue for the current-set-point indicated as i_(cmd). It is this inputvariable that is usable for more advanced control schemes. The firstlevel of improvement for the control is to replace the simple constantvalue with a value that changes between a number of different values;for two conditions an example is: a low value i_(cmd-low) and a highvalue i_(cmd-high). The low value is used when recharging thesuper-capacitors and the high value is used when the super-capacitorsare potentially going to provide power to the load. By proper setting ofthese two values for a given application, the controller ensures thatthere is never a condition where the super-capacitors are operating inconditions that will result in lower charge-capacity and/or lowerenergy-capacity. The value for i_(cmd) can even be used to effectivelydisable the converter operation under certain operating conditions inwhich that mode of operation can improve system efficiency. Forinstance, i_(cmd) can be set to disable current flow from the capacitorsbetween the high and low current-set-point thresholds so that thebattery supplies the load instead of the capacitors when it is moreefficient to do so. Hence, the system designer is able to configure thesystem for efficient operation that provides all of the benefits of ahybrid system for load leveling, reduced stress and better reliabilityfor the battery. And, it does this without needlessly wasting batterycapacity.

Additional refinements on the control can then be added by making thei_(cmd-low) and i_(cmd-high) set-points functions of other systemvariables. For example, the low current set-point, which is relevant forcharging the super-capacitors, can be made a function of thesuper-capacitor charge voltage and it may be desirable to increase theset-point level if the capacitor voltage gets too low. This will helpprevent the super-capacitors from becoming fully discharged. Hence,battery energy capacity may be sacrificed a little bit to ensure thatthe hybrid system capability is available when needed.

Various other control refinements can be made by utilizing the abovecontrol structure, and these details may depend heavily on theapplication. For example, advanced algorithms can analyze the recentload profile history to either identify expected modes of operation, orto just classify the load type. The controller settings can then beautomatically adjusted based on the result. For example, if anaggressive mode of operation is predicted, then the state of charge onthe capacitors may be set at a higher level than under nominal operatingconditions.

Power Converter

The Switch Controller in combination with the Switches in theBi-directional Switching Converter subsystemr in FIG. 2 form abidirectional boost/buck dc/dc converter capable of moving energy backand forth between the internal high voltage bus and the internal lowvoltage bus. The converter allows maximum utilization of the storedenergy in the capacitor by allowing the capacitor voltage to vary widelyduring discharge while maintaining a regulated bus voltage that willnominally match the battery stack voltage. FIG. 3 shows that a typicaltopology consists of single half bridge switching module along withappropriate filter components. The capacitor module can be connected tothe low voltage side of the converter, V_(LV), and the internal highvoltage bus is connected to the high side of the converter, V_(HV),which is typically a battery voltage stack. It should be noted that itis also possible to connect the capacitors to the high voltage side ofthe converter and the bus to the low voltage side if enough capacitorsare stacked in series to yield a voltage larger than the bus, withoutchanging the validity of the approaches discussed here. Operating theswitches at a duty cycle that is equal to the ratio between the high andlow voltage sources is the nominal balanced operation. Increasing theduty cycle results in a buck operation where current is forced into thelow voltage capacitor bank from V_(HV), thereby charging the capacitors.Decreasing the duty cycle will result in boost operation where currentis supplied to the high voltage bus from the capacitor bank, therebyrelieving load on the battery stack.

The controller can therefore alter the switch duty cycle as part of aclosed loop control algorithm such that energy can be transferred to orfrom the high voltage bus (V_(HV)) and therefore it can compensate fortransients on the high voltage bus. Typical efficiencies for such aconverter are in the range of 94%.

The power electronics architecture is scalable in that multiple parallelphases can be added to increase power levels and distribute thecapacitor output current so as not to overload a particular phase. Thisespecially important as the capacitors discharge, since a decreasingvoltage on the capacitor stack results in an increase of current throughthe converter for constant power internal dc bus loads. The controllercan also use the parallel phases to increase the effective switchingfrequency of the system by synchronizing and interleaving the phases.FIG. 4 shows a three phase, two level, converter and FIG. 5 shows theinterleaved and resulting total current waveforms. The total currentwaveform has significantly reduced current ripple and the ripplefrequency has been increased by a factor of three. This reduces theamplitude of the harmonics and increases their frequency which is moreeasily removed by the filtering components in the converter. Furtherincreasing the number of phases will further increase the effectiveswitching frequency. In addition, the additional phases can be commandedindependently by a high bandwidth controller, thereby increasing theresponse time of the system to transient loading.

Switch Controller

There are a number of switch control configurations that can beinvestigated for this application. One of the simplest methods is shownin FIG. 2. The output of the Voltage Controller, D[n], is input to a PWMblock that quantizes the signal and pulse width modulates it to yieldsignal s(t) that is suitable to operate the switches in the PowerConverter, thereby regulating the battery current and the bus voltage.The need for a fast response to transients is addressed by a combinationof feed forward and feedback control found in the Voltage Controller andCurrent Controller systems.

Further improvement in performance can be achieved by modifying theSwitch Controller to include closed loop controllers that regulate thephase current through each phase inductor, Iph_(n), as shown in FIG. 4.In addition, in the work here, the controller can be partitioned intosynchronized time slices such that each phase of the inverter canimmediately respond to commanded voltage changes. In this way, theoverall inverter response time is not limited by the fundamentalswitching frequency of the component switch. FIG. 6 is a block diagramof the control structure that illustrates the concept.

In developing the controller, for a specific application, there is adesign tradeoff between the increased effective bandwidth versus theadded hardware. This choice will also be affected by the type ofinverter switching element, with IGBTs (about 20 kHz), and MOSFETs(>100's kHz) the industry standards, and others possible. Anotheradvantage of the individual phase control is robustness to a failed orunbalanced phase since the command synchronizer can skip a disabledphase or adjust its gains or voltage to compensate for an unbalancedphase.

FIG. 7, as noted above, depicts a second embodiment of a non-limitingexample of a hybrid system according to the teachings of the presentinvention with output DC/DC converter that allows a range of output loadvoltages. FIG. 7 illustrates a block diagram of one design topology forthe hybrid battery system. A feature of this topology is that the outputvoltage of the system is not constrained by the output voltage of thebattery cell bank 202 and can be set by the output dc/dc converter 210as appropriate for varied load requirements.

In this example, the system is controlled by a microprocessor or microcontroller 208, preferably an ultra-low power microprocessor or microcontroller 208, which allows low power monitoring modes withoutsignificantly draining the battery energy. Once a power load is appliedto the battery 202, the microprocessor or micro controller 208 quicklyactivates and enables an advance control mode. With monitoring of theenergy states of the super-capacitor block 204 (which, in a non-limitingexample, could be a Lithium Ion Capacitor (LIC) cell bank in seriesand/or parallel combination) and battery banks 202, as well as thetemperatures, load voltages and currents, the DC/DC converter 206 isable to provide the optimum power delivery from the battery 202 and thesuper-capacitor block 204. The optimum power delivered from thesuper-capacitor and battery combination is input to an output DC/DCconverter 210 that can boost or buck its input voltage such that itsoutput voltage on the output terminals is adjusted to match the load.When the power load-conditions are light enough, the capacitors in thesuper-capacitor block 204 automatically recharge, via the DC/DCconverter 206 in a reverse energy flow mode. In this setup, thesuper-capacitor block 204 discharges in a forward energy flow mode. Themicroprocessor or micro controller 208 allows the incorporation ofadvanced decision making based on existing environmental and loadconditions.

FIG. 8 depicts an overview of the system feedback control model forforward boost, reverse buck operation with outer current controller andwithout inner loop voltage controller. The diagram indicates that thecontroller is a digital discrete time system with discrete timeindicated by n. A moderately high-speed PWM frequency is used to providea good compromise between the size of magnetic components and conversionefficiency. The PWM generator allows a discrete number of steps (i.e.the quantizer) and drives MOSFET switches to control the system dutycycle. The diagram shows the control section the current feedback loopusing a PI controller, although other types of controllers can also beapplied. Referencing the PI Current Controller subsystem, the blockslabeled G_(PC), Integrator, and G_(IC) form the PI controller for thecurrent control loop, with G_(PC) being the proportional gain and G_(IC)being the integral gain. The block labeled LPF is a low pass filter usedprior to sampling the input signals. The ZOH blocks are zero order holdsand are typical sample and hold operations for a digital controller. TheSaturation with enable block is a signal limiter that only allows theinput signal to pass through the block if it is within the prescribedmaximum and minimum values. Otherwise, the output of that block islimited to the maximum or minimum value allowed. The Switch Controllersubsystem features a PWM generator which generates varying duty cycleswitching commands based on the input signal D[n]. The switchingcommands operate the Switches in the Bi-directional Switching Convertersubsystem. The switches control the flow of current between the battery,super-capacitors, and load. The system monitors the capacitor bankvoltage and uses it to provide a feed forward signal into the voltagecontroller. The battery current is monitored and used as the inputmeasurement for the current controller, while the load voltage ismonitored and used as the input measurement for the voltage controller.Relevant filtering and sampling are as shown.

Typically, the controller sample frequency F_(control) would be at amultiple sub-division of the PWM frequency F_(switch). It can be seenthat the controller must generate the PWM signal s(t) in order to drivethe switches. However, the controller itself needs to only generate theduty cycle D[n], and a PWM generator can generate the actual analogsignal. The duty cycle D[n] and switch control signal s(t) are relatedto each other by the following mathematical formulas, noting thatn=└t·F_(control)┘, where the half bracket/bar notation means the floorfunction, or rounding down to the lower integer value.

${D\lbrack n\rbrack} = {\left. {F_{conrol} \cdot {\int_{\frac{n}{F_{control}}}^{\frac{n + 1}{F_{control}}}{{s(t)} \cdot {dt}}}}\Leftrightarrow{s(t)} \right. = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu} \left( {{t \cdot F_{switch}} - \left\lfloor {t \cdot F_{switch}} \right\rfloor} \right)} \geq {D\lbrack n\rbrack}} \\1 & {otherwise}\end{matrix} \right.}$

This system has a PWM generator that is capable of generating aparticular quantization of discrete duty cycles in the range of 0 to 1.This resolution limit can introduce noticeable variation of the outputcontrol if the resolution in the quantizer is too low, hence some effortcould be made to ensure adequate resolution, or allow the PWM generatorto alter the duty cycle during the discrete time interval n, so that theaverage duty cycle takes on fraction values between the allowedresolution steps.

The command for the PWM generator is limited by a saturation-block. Forexample, a tolerance band around the feed forward value can be used. Thesaturation block generates an enable signal for the integrator, whichhalts integration if a limit is hit. The controller must also monitorseveral circuit variables by sampling with A/D converters at thecontroller rate, and the controller is digitally implemented as a PIcontroller, as shown. If the current control loop tries to commandvalues outside the allowed duty cycle range, the saturation block limitsthe command (range is D_(low) to D_(high)) and disables the integrator.The outer current control loop monitors the battery current to maintaina level current draw from the battery.

The PI controller also utilizes a feed forward signal to improve systemresponse but the feed forward may be omitted in less demanding controlapplications. The inner voltage feed forward uses the measured voltageand the value of the input capacitor voltage to estimate the typicalduty cycle that would be needed to generate that output voltage underthose conditions. It can be seen that the calculation of estimated dutycycle is simply the ratio of output voltage to input voltage, as istypically expected in a boost converter. The current control loop usesan estimated value or typical value for the commanded voltage. In thisimplementation, the feed forward value is just a pre-stored constantV_(ff); however, a real system could keep a record of the estimatedremaining battery capacity (by monitoring and integrating batterycurrent, with considerations for temperature etc.) and use measuredbattery temperature, along with a formula or look-up table to estimatethe expected output voltage. The current loop also uses a commandedcurrent value, which can be a pre-stored value based on the expectedload profile, or could be an adjustable value by the user. Essentially,a real implementation can use the microcontroller to provide additionalintelligence to aid the feedback loops in performing their functions.

It should be noted that the controller in FIG. 8 has an input commandvalue for the current-set-point indicated as i_(cmd). It is this inputvariable that is usable for more advanced control schemes. The firstlevel of improvement for the control is to replace the simple constantvalue with a value that changes between a number of different values;for two conditions an example is: a low value i_(cmd-low) and a highvalue i_(cmd-high). The low value is used when recharging thesuper-capacitors and the high value is used when the super-capacitorsare potentially going to provide power to the load. By proper setting ofthese two values for a given application, the controller ensures thatthere is never a condition where the super-capacitors are operating inconditions that will result in lower charge-capacity and/or lowerenergy-capacity. The value for i_(cmd) can even be used to effectivelydisable the converter operation under certain operating conditions inwhich that mode of operation can improve system efficiency. Forinstance, i_(cmd) can be set to disable current flow from the capacitorsbetween the high and low current-set-point thresholds so that thebattery supplies the load instead of the capacitors when it is moreefficient to do so. Hence, the system designer is able to configure thesystem for efficient operation that provides all of the benefits of ahybrid system for load leveling, reduced stress and better reliabilityfor the battery. And, it does this without needlessly wasting batterycapacity.

Additional refinements on the control can then be added by making thei_(cmd-low) and i_(cmd-high) set-points functions of other systemvariables. For example, the low current set-point, which is relevant forcharging the super-capacitors, can be made a function of thesuper-capacitor charge voltage and it may be desirable to increase theset-point level if the capacitor voltage gets too low. This will helpprevent the super-capacitors from becoming fully discharged. Hence,battery energy capacity may be sacrificed a little bit to ensure thatthe hybrid system capability is available when needed.

Various other control refinements can be made by utilizing the abovecontrol structure, and these details may depend heavily on theapplication. For example, advanced algorithms can analyze the recentload profile history to either identify expected modes of operation, orto just classify the load type. The controller settings can then beautomatically adjusted based on the result. For example, if anaggressive mode of operation is predicted, then the state of charge onthe capacitors may be set at a higher level than under nominal operatingconditions.

An application of the hybrid system is to provide a high energy highpower portable power source to replace and/or enhance the performance ofa standard BA-5590 battery pack. This unit is typically carried bysoldiers and used to power portable devices such as communicationsdevices. The need for high power bursts during communications, forexample, are well addressed by the hybrid super-capacitor batterysystem. FIG. 9A shows the typical interconnection between a standardBA-5590 and a Load Device. FIG. 9B illustrates the replacement of thestandard BA-5590 with the Hybrid BA-5590. Notice that the Batteries arenow supplemented by the DC/DC converter and super-capacitors asdescribed above. FIG. 9C illustrates how the hybrid system here can beused as an external enhancement to a standard BA-5590. In thisimplementation, the Hybridization Module is externally connected inseries with the BA-5590. FIG. 9D illustrates another embodiment of thehybrid system, but with the Hybridization Module incorporated into theLoad Device. In each case, the physical location of the hybridcomponents is changed but the overall system is the same as describedabove.

FIG. 10 illustrates the discharge performance improvement that can berealized using the hybrid system with a pulsed power load. The lightgray plot is the output voltage of a 5-cell battery stack as compared tothe black plot output voltage of a hybrid super-capacitor/5 cell batterystack. The tests were performed operating at −20° C. with a nominaloutput voltage of 12V. This empirical data was measured for an operatingsystem with a pulsing power load between 20 W (10% of the time) and 6 W(90% of the time), but is indicative of similar performance at higherpower levels. The super-capacitor is effective in providing high pulsepower and is recharged from the batteries during the time that the loadrequires 6 W. Over time, energy is drawn from the system and the outputvoltage diminishes. The test is considered to be completed when theoutput voltage reaches 10V. It can be seen that the battery-only systemis discharged in about 5 hours while the hybrid system is discharged inapproximately 14 hours. The hybrid system has reduced stress on thebatteries and it operates almost 3× longer than with the batteriesalone.

FIG. 11 illustrates a preferred embodiment of the hybridsuper-capacitor/batteries system that is form and fit compatible with astandard BA-5590 battery pack. This configuration corresponds to thecase shown in FIG. 9B. A feature of this system is that the controllerand super-capacitor are field separable from the battery compartment.Once spent, the batteries can be removed and discarded while thesuper-capacitor and control circuitry can be used again with a new setof batteries. This replacement can also be performed in the field.

It should be noted that as technology advances, the hybrid techniquesand controls presented here can be applied to other combinations ofsources when one source has high energy capability but lower powercapability and the other source has higher power capability and lowerenergy capability (relative to each other). For example, another similarhybrid combination is fuel cell as the high energy source and thesuper-capacitors as the high power source. In the following discussion,the hybrid system consists of batteries as the high energy source andsuper-capacitors as the high power capability source. It should also benoted that the hybrid architecture is not limited to only two powersources but can be a hybrid of a multitude of power sources, each withdifferent energy/power capabilities.

The various embodiments described above are provided by way ofillustration only and should not be construed to limit the scope of thedisclosure. Those skilled in the art will readily recognize variousmodifications and changes that may be made to the principles describedherein without following the example embodiments and applicationsillustrated and described herein, and without departing from the spiritand scope of the disclosure.

The development of a hybrid system featuring high energy density andhigh-power density for primary battery cells has been demonstrated by usin the prior patent entitled, “Design for Hybrid Super-Capacitor/BatterySystems in Pulsed Power Applications” (U.S. application Ser. No.14/279,687 filed May 16, 2014). There, the hybrid technology utilizinglithium ion batteries and lithium ion super-capacitors featured abidirectional dc/dc converter that controlled the battery current suchthat pulsed power loads are supplied by the super-capacitor to minimizestress on the batteries. That system excelled in significantly extendinglifetime and performance over a battery-only system with loads requiringpulse power profiles. The hybrid approach demonstrated in testing theability to support SATCOM military communications profiles where batteryonly approaches failed.

The current patent application extends that hybrid system by modifyingthe control algorithm such that the super-capacitor can not only supplypulsed power, but it now can also absorb pulsed power from the loadwhile keeping the battery current constant such that the incoming pulsedpower does not stress the battery. The absorbed energy is accumulated inthe capacitor and then the control algorithm operates the dc/dcconverter to recharge the battery with the energy from the capacitor ata rate that optimized battery performance. If the current from the loadto the hybrid system is within the optimal operating range of thebattery, then the hybrid system will allow the load to directly chargethe battery. This hybrid system keeps the battery current operating inits most efficient range during both discharging and charging (thedischarging and charging currents may be different values) by using thesuper-capacitor to supply or absorb pulsed in energy that wouldotherwise stress the rechargeable battery and result in reduced batterycycle life and/or reduced effective capacity over time. The applicationsfor this hybrid system include quick charge and carry, regenerativeenergy from the load, and energy harvesting. Whereas the prior hybridsystem was directly applicable to portable power such as the BA-5590family of primary battery cell packs, this system is now also directlyapplicable to rechargeable portable power such as the BB-2590 family ofrechargeable battery cell packs.

Our previous work in the development of the Hybrid system mainlyconsidered primary cells and so power or energy was flowing out of thesystem to the load. Extending that focus to hybrid integration for arechargeable battery cell system significantly increases complexity asanother dimension of power or energy flow is introduced. The latestrevision of the hybrid system has circuitry and algorithms that havebeen extended to allow for power flow into and out of each of thesystems interfaces. These interfaces include the battery interface,super-capacitor interface, and the external load interface which is thepoint in the circuit in which either an external source or sink isconnected. The DC/DC converter is a bidirectional converter that allowsenergy to flow into the super-capacitor or out of the super-capacitor.FIG. 12 depicts the basic elements of the hybrid system as describedabove. Note that the battery can directly supply or absorb (recharge)energy from the load if that energy is at a low enough rate such that itdoes not stress the battery. This hybrid system for rechargeables doesallow charging directly to the battery from the load. The capacitorkeeps the battery current in an optimal operating range and thecapacitor will absorb any additional energy (for example high pulsedcurrent) as required. High power discharging and/or absorbing to/fromthe load is first routed to the super-capacitor via the bidirectionalconverter. The energy is then moved from/to the super-capacitor to/fromthe battery at a slower rate to optimize the battery's performance.

The hybrid controller may be organized into several separate softwarestructures that promote optimization and allow for development of eachaspect of the system separately and efficiently. The defined softwarestructures as indicated in FIG. 13 include the battery managementsystem, LIC management system, load or external interface managementsystem, and hybrid controller. The battery management system maintainsvoltage, current, and temperature measurements and uses these quantitiesto identify the state and health of the batteries. For example,battery's state of charge is monitored by its voltage and current loadover time so that the system can determine when the battery can accept arecharge and when it can source energy. The optimum current to/from thebattery can be temperature dependent and thus can be automaticallyadapted to changes in temperature. In addition, if the battery iscomposed of a number of series connected cells, charge balancing betweenthe cells may be required and incorporated into this system. Likewise,the LIC management system collects voltage and temperature measurementsand uses these to also determine LIC state and health. This component ofthe algorithm, then, indicates the state of charge of the capacitor anddetermines when it can source or sink energy. The load management systemhas the capability of collecting voltage and current data to determinethe state of the external load. If the load requires energy, the hybridwill supply it, if it is regenerating energy, the hybrid will absorb it.Note that if the external load is supplying energy and thesuper-capacitor is fully charged and the battery is either fully chargedor cannot accept the energy at a high enough rate, then the hybrid hasswitch hardware that can disconnect the load to prevent damage to theunit. Lastly, the hybrid controller structure is responsible forsampling the system measurements, available through each of themanagement systems, and using them to determine how to manipulate theDC/DC converter to control power flow. Development of this control wascompleted in our previous patent work (U.S. application Ser. No.14/279,687 filed May 16, 2014); however, this controller is furtheradvanced with the added implementation of the other structuredmanagement systems to handle each of the systems components and makedecisions about their state and health.

A distinguishing feature of this hybrid controller is the integration ofbattery management, the capacitor management, and the load managementwith the hybrid controller to route bidirectional power and energy suchthat battery stress is reduced and system performance is optimized,especially in terms of cycle life, effective capacity, and reducedoperating temperature. The system is effective whether it is supplyingor absorbing energy. The integration of these subsystems and thedecision making for routing power and energy is implemented in thesoftware algorithm using a state machine.

Each element of the Hybrid system is capable of existing in one of thefollowing power flow states: charging, discharging, isolated. Allcombinations result in a total of 27 possible hybrid states in which thesystem may exist. Of the 27 possible hybrid states, only 13 may existdue to the conservation of energy. Each of the states are discussedbelow in terms of each of the systems elements with the DC/DC converteromitted for simplification. Arrows 1402 indicate energy flowing out(discharge) of the element, arrows 1404 indicate energy flowing into(charge) the element, and the solid black line 1406 indicates no energyflow (isolated). The states are identified with a name describing theflow of energy in FIGS. 14A-M.

Of the 13 possible hybrid states, there are three classifications asfollows: Source, Harvest, and Idle. Source states supply energy throughthe hybrid system to an external load. Harvest states collect energythrough the hybrid system from an external source or charger. Idlestates isolate the Load interface from the outside world and arerestricted to energy flow between the battery and super-capacitorinternal to the hybrid system. This classification of states is known asthe Hybrid mode. To determine the present state of the hybrid system,additional pieces of information about the conditions present in thesystem must be known. These conditions include detected energy flow,system energy priority, battery state of charge, and super-capacitorstate of charge. Flow is defined by the direction energy is moving atthe Load interface. Energy priority is given to either the battery orthe super-capacitor. When in Source mode or Idle mode, priority is givento the super-capacitor by default; and when in Harvest mode, energypriority is given to the battery by default. The hybrid is also designedsuch that the user may manually select the energy priority of the systemas the necessary priority may be situationally dependent for the user.This feature allows freedom for the user to maintain maximum energy ineither the high power or high energy element of the system. Battery andsuper-capacitor state of charge are determined in the management systemsand are classified as charged, discharged, or dynamic. From theseconditions the hybrid state machine is developed, however it is fairlycomplicated to represent graphically and so a diagram is omitted. Thestate machine automatically transitions the hybrid system into theappropriate state such that all elements of the system are operatedwithin their limits and are protected from dangerous conditions. Thestate machine transitions freely based on the defined conditions unlessa fault condition is detected within management system in which case aspecific state is forced that addresses the specific fault condition.The hybrid state machine has been implemented in software to ensureflawless transition between states as all combinations of the governingconditions are applied to the system.

The performance improvement using the hybrid system is evident in thefollowing sections. In terms of physical arrangement and packing, thehybridization of a battery system can be achieved by an external orinternal physical configuration, as shown in U.S patent application Ser.No. 14/279,687. With the external configuration, the battery pack isseparate from the hybrid controller board and the super-capacitor.Interconnection with proper cabling allows hybridization to take place.With the internal configuration, the package is designed so thebatteries, the hybrid control board, and the super-capacitor are allinside the same physical package. Connections between them are withinternal cables. Both the internal and external configurations aresupported in this extended work. In a preferred embodiment, the hybridsystem developed for primary cells hybridizes the standard BA-x590family power packs or equivalent and the hybrid system for rechargeablecells presented here hybridizes the standard BB-2590 family power packsor equivalent.

One method for visualizing the mechanism by which the hybrid enablesbenefit in the battery system is through the use of energy densitydistribution mappings for particular battery chemistries of interest.FIG. 15 shows the energy density distribution for the alkaline chemistrydistribution as a function of discharge rate and ambient temperature.Normalization of the data effectively yields the efficiency of thebattery over the desired operating range. Propagation towards the regionlabeled 1502 indicates a decrease in battery efficiency whileprogression towards the region labeled 1504 indicates operation at highefficiency. In a battery only system, as is the case without the hybridsystem, the battery is forced to operate at particular operating pointsdictated by the load since they are directly coupled. In the hybridsystem, the super-capacitor, an element that is very efficient at highpower, supports the peak power pulse of the load while maintaining thebattery at lower power within its high efficiency region. The batterythen recharges the super-capacitor while the load is drawing less powerwhich also allows the battery to remain in an efficient region. Thishybrid solution provides decoupling between the load and batteryallowing flexibility to operate the battery within its more efficientregion of operation. The same amount of energy is delivered to the load,however, the manner in which the energy is delivered allows for a moreefficient transfer and less waste at the battery extending its lifetime.In addition to extending battery lifetime, improving battery efficiencyand minimizing the peak to mean power or current demanded from thebattery also reduces battery stress and heating. This lessens thelikelihood of a catastrophic breakdown or instability within the batteryas lithium batteries are known to demonstrate violent behavior understressful conditions. Reducing stress and heating on the battery is alsohighly beneficial for rechargeable cells as the deterioration of itselectrodes and depletion rate of its capacity may be slowed to improvecycle life. The demonstrated improvement using the hybrid system is abasis for the development of the hybrid algorithm with advanced controland system infrastructure presented in this work.

The Samsung ICR18650-26A rechargeable cells performance testing wasrepeated with increasing cycles. The two experimental test sets were thebattery-only approach and the hybrid approach which placed two differentrepresentative load profiles on the cells under test. The battery-onlyapproach featured a more dynamic profile with a higher peak currentlevel while the hybrid approach exhibited a constant current profile.Each profile over a single cycle transferred the same amount of energyhowever the rate at which the energy was transferred is different. It isin the differences of the transfer rate in which benefit may beachieved.

Evidence to support the benefit achieved through use of the hybridapproach over the battery-only approach is evident in FIG. 16, FIG. 17,and FIG. 18. The hybrid achieves greater discharge capacity as shown inFIG. 16, greater charge capacity as shown in FIG. 17, and cooleroperating temperature as shown in FIG. 18. The difference in the chargecapacity is indicative of greater degradation taking place in thebattery-only approach cell as the charge method for each case is thesame. As cycling continues the differences in the rate of degradationpresent in the two approaches are expected to become more evidentfurther demonstrating the benefit achieved through the hybrid approach.

The study of the Samsung ICR18650-26A lithium ion rechargeable cells,which are present in the BB2590 rechargeable battery pack, has producedresults that manifest hybrid benefit over battery-only approaches.Improvements were seen in achieved charge and discharge capacity on acycle by cycle basis. Cell operating temperature was also seen to bereduced in the case of the hybrid which is an important factor in slowlythe rate of battery degradation. The energy gained when using the hybridsystem increases over the cycle life of the battery.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of anyinvention or of what may be claimed, but rather as descriptions offeatures that may be specific to particular embodiments of particularinventions. Certain features that are described in this specification inthe context of separate embodiments can also be implemented incombination in a single embodiment. Conversely, various features thatare described in the context of a single embodiment can also beimplemented in multiple embodiments separately or in any suitablesubcombination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asubcombination or variation of a sub combination.

CONCLUSION

A system and method has been shown in the above embodiments for theeffective implementation of a novel design for hybridsuper-capacitor/rechargeable battery system. While various preferredembodiments have been shown and described, it will be understood thatthere is no intent to limit the invention by such disclosure, butrather, it is intended to cover all modifications falling within thespirit and scope of the invention, as defined in the appended claims.For example, the present invention should not be limited by specifichardware used to implement the various controllers described within thisdisclosure.

1. A system comprising: a hybrid super-capacitor/battery systemcomprising a super-capacitor unit comprising one or moresuper-capacitors and a battery unit connected to a load, the batteryunit comprising one or more battery cells rated at a battery outputvoltage; a DC/DC converter connected to said super-capacitor unit andsaid battery unit, the DC/DC converter allowing charging and dischargingof said super-capacitors; and a hybrid algorithm comprising: a batterymanagement system, a super-capacitor management system, a loadmanagement system, and a hybrid controller, the battery managementsystem collecting a first set of data comprising voltage, current, andtemperature measurements associated with the battery unit, andidentifying a state and health of the battery unit based on the firstset of data, the super-capacitor management system collecting a secondset of data comprising voltage and temperature measurements associatedwith the super-capacitor, and determining a super-capacitor state andhealth based on the second set of data, the load management systemcollecting a third set of data comprising voltage and current dataassociated with the load, and determining a state of the load based onthe third set of data, the hybrid controller sampling systemmeasurements available through the battery management system, thesuper-capacitor management system, and the load management system, andmanipulating the DC/DC converter to control power flow, whereinintegration of the battery management system, the super-capacitormanagement, and the load management system with the hybrid controllerroutes bidirectional power and energy such that battery stress isreduced, and system performance is optimized, and wherein the system iseffective whether it is supplying or absorbing energy.
 2. The system ofclaim 1, wherein the hybrid algorithm is implemented at least in partusing a state machine.
 3. The system of claim 1, wherein the battery'sstate of charge is monitored by its voltage and current load over timeso that the system can determine when the battery accepts a recharge orwhen it sources energy.
 4. The system of claim 1, wherein optimumcurrent to/from the battery is temperature dependent and isautomatically adapted to changes in temperature.
 5. The system of claim1, wherein when the battery is composed of a number of series connectedcells, and the system further conducts charge balancing between theseries connected cells.
 6. The system of claim 1, wherein when the loadis supplying energy and the super-capacitor is fully charged and thebattery is either fully charged or cannot accept the energy at a highenough rate, then the system further comprises switch hardware thatdisconnects the load to prevent damage.
 7. The system of claim 1,wherein said super-capacitors are one or more of, or combinations of,the following: Electric Double Layer Capacitor (EDLC) or Lithium IonCapacitor (LiC).
 8. The system of claim 1, wherein said battery cellscomprise at least one fuel cell.
 9. A system comprising: a hybridsuper-capacitor/battery system comprising a super-capacitor unitcomprising one or more super-capacitors and a battery unit connected toa load, the battery unit comprising one or more battery cells rated at abattery output voltage; a DC/DC converter connected to saidsuper-capacitor unit and said battery unit, the DC/DC converter allowingcharging and discharging of said super-capacitors; and a hybridalgorithm comprising: a battery management system, a super-capacitormanagement system, a load management system, and a hybrid controller,the battery management system collecting a first set of data comprisingvoltage, current, and temperature measurements associated with thebattery unit, and identifying a state and health of the battery unitbased on the first set of data, the super-capacitor management systemcollecting a second set of data comprising voltage and temperaturemeasurements associated with the super-capacitor, determining asuper-capacitor state and health based on the second set of data, and,based on collected second set of data, determining when energy should besourced or sinked, the load management system collecting a third set ofdata comprising voltage and current data associated with the load, anddetermining a state of the load based on the third set of data, thehybrid controller sampling system measurements available through thebattery management system, the super-capacitor management system, andthe load management system, and manipulating the DC/DC converter tocontrol power flow, wherein integration of the battery managementsystem, the super-capacitor management, and the load management systemwith the hybrid controller routes bidirectional power and energy suchthat battery stress is reduced, and system performance is optimized withregards to any of, or a combination of, the following parameters: cyclelife, effective capacity, and reduced operating temperature, and whereinthe system is equally effective whether it is supplying or absorbingenergy.
 10. The system of claim 9, wherein the hybrid algorithm isimplemented at least in part using a state machine.
 11. The system ofclaim 9, wherein the battery's state of charge is monitored by itsvoltage and current load over time so that the system can determine whenthe battery accepts a recharge or when it sources energy.
 12. The systemof claim 9, wherein optimum current to/from the battery is temperaturedependent and is automatically adapted to changes in temperature. 13.The system of claim 9, wherein when the battery is composed of a numberof series connected cells, and the system further conducts chargebalancing between the series connected cells.
 14. The system of claim 9,wherein when the load is supplying energy and the super-capacitor isfully charged and the battery is either fully charged or cannot acceptthe energy at a high enough rate, then the system further comprisesswitch hardware that disconnects the load to prevent damage.
 15. Thesystem of claim 9, wherein said super-capacitors are one or more of, orcombinations of, the following: Electric Double Layer Capacitor (EDLC)or Lithium Ion Capacitor (LiC).
 16. The system of claim 9, wherein saidbattery cells comprise at least one fuel cell.
 17. A system comprising:a hybrid super-capacitor/battery system comprising a super-capacitorunit comprising one or more super-capacitors and a battery unitconnected to a load, the battery unit comprising one or more batterycells rated at a battery output voltage; a DC/DC converter connected tosaid super-capacitor unit and said battery unit, the DC/DC converterallowing charging and discharging of said super-capacitors; and astorage medium comprising computer readable program code which whenexecuted by a processor implements a hybrid algorithm comprising: abattery management system, a super-capacitor management system, a loadmanagement system, and a hybrid controller, the storage mediumcomprising: computer readable program code which when executed by theprocessor implements the battery management system collecting a firstset of data comprising voltage, current, and temperature measurementsassociated with the battery unit, and identifying a state and health ofthe battery unit based on the first set of data, computer readableprogram code which when executed by the processor implements thesuper-capacitor management system collecting a second set of datacomprising voltage and temperature measurements associated with thesuper-capacitor, determining a super-capacitor state and health based onthe second set of data, and, based on collected second set of data,determining when energy should be sourced or sinked, computer readableprogram code which when executed by the processor implements the loadmanagement system collecting a third set of data comprising voltage andcurrent data associated with the load, and determining a state of theload based on the third set of data, computer readable program codewhich when executed by the processor implements the hybrid controllersampling system measurements available through the battery managementsystem, the super-capacitor management system, and the load managementsystem, and manipulating the DC/DC converter to control power flow,wherein integration of the battery management system, thesuper-capacitor management, and the load management system with thehybrid controller routes bidirectional power and energy such thatbattery stress is reduced, and system performance is optimized withregards to any of, or a combination of, the following parameters: cyclelife, effective capacity, and reduced operating temperature, and whereinthe system is equally effective whether it is supplying or absorbingenergy.
 18. The system of claim 17, wherein said super-capacitors areone or more of, or combinations of, the following: Electric Double LayerCapacitor (EDLC) or Lithium Ion Capacitor (LiC).
 19. The system of claim17, wherein the hybrid algorithm is implemented at least in part using astate machine.